In the event of a written protest against the proposed amendment signed and acknowledged by the owners of 20% of the frontage proposed to be altered, or by the owners of 20% of the frontage immediately adjoining or across the alley or rear line therefrom, or by the owners of 20% of the frontage directly opposite the frontage proposed to be altered as to such regulations or zoning district, and filed with the City Clerk, such amendment shall not be passed except by the favorable vote of three-fourths of all the members of the City Council.
('71 Code, § 11-21-4) (Ord. 1413, passed 9-13-60)